1. Field
The disclosed concept relates to vacuum switching apparatus such as, for example, vacuum switches including a vacuum envelope such as, for example, vacuum interrupters. The disclosed concept also pertains to hybrid switch assemblies for vacuum interrupters.
2. Background Information
Vacuum interrupters include separable main contacts disposed within an insulated and hermetically sealed vacuum chamber. The vacuum chamber typically includes, for example and without limitation, a number of sections of ceramics (e.g., without limitation, a number of tubular ceramic portions) for electrical insulation capped by a number of end members (e.g., without limitation, metal components, such as metal end plates; end caps; seal cups) to form an envelope in which a partial vacuum may be drawn. The example ceramic section is typically cylindrical; however, other suitable cross-sectional shapes may be used. Two end members are typically employed. Where there are multiple ceramic sections, an internal center shield is disposed between the example ceramic sections.
Two types of vacuum interrupters include, for example, Radial Magnetic Field (RMF) vacuum interrupters, also commonly referred to as Transverse Magnetic Field (TMF) vacuum interrupters, and Axial Magnetic Field (AMF) vacuum interrupters. RMF vacuum interrupters typically include a radial magnetic field generating mechanism such as, for example and without limitation, a spiral contact (see, for example, U.S. Pat. Nos. 2,949,520; 3,522,399; and 3,809,836) or a contrate cup (see, for example, U.S. Pat. Nos. 3,089,936; 3,836,740; and 4,390,762). This structure is designed to force rotation of the arc column between the pair of electrical contacts interrupting a high current, thereby spreading the arcing duty over a relatively wide area. AMF vacuum interrupters, on the other hand, are typically structured to force current through a long coil-shaped path having a relatively significant circular rotational component in order to maintain the arc in a diffused state. See, for example, U.S. Pat. Nos. 5,804,788; 6,080,952; and 7,721,428.
Both RMF and AMF switch assemblies suffer from a number of disadvantages. For example, the single running columnar arc of RMF designs only spreads the arcing duty over the outer section of a normally circular shaped contact surface. Therefore, the heavy burning at the arc root of the single columnar arc carrying the entire short-circuit current eventually limits the dielectric recovery ability of the contact gap. With AMF vacuum interrupters, the continuous current carrying capability of the vacuum interrupter is limited due to the relatively long current path and corresponding electrical resistance to the current flow.
In an attempt to address the foregoing disadvantages, U.S. Pat. Nos. RE32,116 and 4,636,600, for example, disclose vacuum interrupters in which the axial magnetic field is generated, not by a long circular current flow path, but rather with strategic placement of ferromagnetic parts, such as a horseshoe assembly of magnetic plates.
U.S. Pat. Nos. 4,445,015; 4,553,002; 4,675,482; and 4,717,797, for example, disclose adding an axial magnetic field generating structure to a contrate cup type RMF structure, to provide enhanced high current interruption capability. However, such structures are complex and relatively large (e.g., tall in the axial direction). Moreover, the axial magnetic field is provided by manipulating the current flow along a relatively long path, resulting in substantial electric resistance of the vacuum interrupter.
There is, therefore, room for improvement in vacuum switches, such as vacuum interrupters, and in hybrid switch assemblies therefor.